Electronic alarm systems have existed for many years which utilize a series of sensors linked to a centralized sensor station. Such sensors might include magnetic or electronic switches which are installed across doors or windows in a home or business. Other sensors might include level or event detectors which provide a signal based upon a predetermined alarm condition. The sensors can be connected or linked to the receiving station in a variety of ways, including hardwired or wireless connections. Wireless connections are often used to eliminate the need for unsightly or difficult to install wiring harnesses during installation. For instance, U.S. Pat. No. 3,969,709 discloses a wireless burglar alarm system which utilizes a remote transmitter to send a high frequency carrier signal, which is indicative of an alarm condition, to a receiver to sound an alarm. U.S. Pat. No. 5,486,812 discloses a similar security arrangement with a control module, an alarm, and a multiplicity of stations. Each station incorporates a detector and a transmitter for sending alarm condition signals to the control module which then indicates an alarm condition. Accordingly, these disclosures alleviate the time and expense required for hard-wiring alarm transmitters and receiver units throughout a building or structure for a given alarm system.
Alternatively, the central sensor station can be used to collect and process the various alarm signals and can thereafter be used to communicate the alarm conditions to the necessary security monitoring center and/or authorities so that appropriate corrective action can be taken. The sensor station signals are transmitted to the security monitoring center via hardwired (e.g. telephone) or wireless (e.g. radio frequency) connections. U.S. Pat. No. 5,319,698 discloses an example of one such system which uses a slave transmitter to provide a signal to a local security station. The security station activates an alarm and/or dials a sequence of telephone numbers to provide a verbal alarm. Another example is shown in U.S. Pat. No. 4,994,787 which discloses an on location base station which latches alarm conditions and retains them until manually reset. A remote station is then used to interrogate the base station to determine whether an alarm has occurred.
In either example system, the transmitter must be powerful enough, or the receiver near enough, so that the signals are received by the security monitoring center. Standard RF transmissions are limited in power and range by the practicality of the system, and Federal laws regulate the transmission of such signals through the air. Lower powered transmitters might be used if a relay system where employed to sequentially boost and re-transmit the alarm signal to the destination security monitoring center. However, such a transmission relay system would be very expensive to construct and maintain.
Alternatively still, many alarm systems do not use wireless signal transmissions and instead communicate with the security monitoring center via telephone line. While this is an inexpensive way to transmit alarm signals over long distances, the telephone connections are susceptible to breakage and sabotage. For instance, a burglar might become familiar with a particular system's usage of phone lines to report alarm conditions and therefore cut the outgoing telephone line. The burglar would then be free to trip the alarm and rob the now unprotected building or structure because the alarm system would have lost its link to the security monitoring center.
As a result, telephone companies are currently forced to use expensive dedicated electronic equipment to monitor telephone lines that are being used for alarm reporting systems. Such hardware monitors the telephone lines relatively frequently, e.g. usually every 15 seconds, to alert the security monitoring center in case of a break or malfunction in the line. The need for such monitoring hardware is further necessitated by the fact that most houses have the telephone line exposed at the point where it enters the external wall of the house and therefore it is easy for a burglar to cut the line before breaking into the dwelling.
The Applicant submits that two-way pager technology might be used for the transmission link between the sensor station and the security monitoring center which would utilize relatively low power, but would still provide effective range. However, the prior art does not presently teach such a solution for alarm systems. U.S. Pat. No. 5,128,979 discloses a personal emergency response system which includes a local response center which pages on-site personnel via individual paging units in response to alarm signals. U.S. Pat. No. 5,278,539 discloses an emergency warning system which utilizes conventional RF or telephonic links between sensor stations and the security monitoring station (Local Emergency Planning Commission--LEPC). The LEPC then sends out various signals via pager transmissions to receiving media locations to thereby initiate warnings to the public. These systems, however, do not teach the implementation and advantages of two-way paging technology as applied to the communication link between the sensor station and security monitoring center.
Accordingly, what is needed in the field is an alarm system which incorporates a communication means between the centralized sensor station and the security monitoring center which is wireless, capable of two-way communication, and yet can transmit a signal over a relatively long distance while using a relatively low-powered transmitter.